PURPOSE: To prevent the wear of a casing by a guide ring and keep a regularly stable operating state by mounting an auxiliary ring formed from a wear resisting material such as reinforced Teflon on the end surface of the guide ring making contact with the inner wall surface of the casing.

CONSTITUTION: An auxiliary ring 2A fitted to the fitting groove 21 on the outer circumferential end surface of a guide ring 2 is formed from a wear resisting material such as reinforced Teflon or a phenol resin rubber, and the guide ring 2 is received in guide ring receiving recessed parts 3B on both sides of a rotor 3, and the auxiliary ring 2A makes contact with the port plate 12 of a casing 1 and the inner wall surface of an end plate 13, respectively. By rotating a rotor 3 at low speed, vanes 4 are rotated while being guided by the guide ring 2 and sucked through a suction hole 12 to discharge a material to be transferred blocked between the vanes 4 through a discharge hole 12B. When the guide ring 2 is pressed and moved, the auxiliary ring 2A is pressed onto the inner wall surface of the casing 1.